In this case, motor/pump units having a separate drive unit have been found to be particularly flexible to use since they can be operated as required independently of the main drive. In this instance, vane pumps and dual diaphragm pumps with two opposing elastomer diaphragms in a horizontally opposed arrangement are particularly widespread. The dual diaphragm pumps particularly have compared with vane pumps advantages that they function in a reliable manner even at high temperatures and at great heights at low air pressure, and further have a steep air flow start-up characteristic. However, they are also in most cases constructed in a heavier, larger, more complex manner and are consequently more expensive than vane pumps. In addition, such constructions often require complex devices in order to protect against water being introduced into the inner space in order to prevent damage to the motor/pump unit and the brake booster.